1. Field of the Invention
The present invention relates to a feeding device and an image forming apparatus having the same, and more particularly, to a technique for separating sheets using an inclined surface separation method.
2. Description of the Related Art
In the past, an image forming apparatus such as an ink jet printer, a laser printer, a fax device, or a copying machine, has included a feeding device for feeding sheets to an image forming unit one by one. As the feeding device, there is an inclined surface separation-type feeding device which is provided with a separation member having a high friction coefficient on an inclined surface to increase separation performance.
FIG. 10 is a cross-sectional view illustrating the configuration of an inclined surface separation-type feeding device according to the related art. In the feeding device 100 illustrated in FIG. 10, sheets S are stacked and stored in a sheet feed tray 101. A feeding roller arm 104 that pivots according to the height of the stacked sheets is provided above the sheet feed tray 101. A feeding roller 105 is mounted on the front end of the feeding roller arm 104 and a drive shaft 106 is mounted to the rear end thereof. The feeding roller arm 104 holds the drive shaft 106 so as to be pivotable, and the rotating force of the drive shaft 106 is transmitted to the feeding roller 105 via gears (not shown). Then, the feeding roller 105 rotates while contacting the uppermost sheet S1 stacked in the sheet feed tray 101 and thus moves the sheet S1 forward.
Forward in the movement direction of the sheet S1, a separation plate 102 is disposed. The separation plate 102 is inclined at an angle of θ (see FIG. 10) which is an obtuse angle with respect to the stacking surface of the sheet S1 in the sheet feed tray 101, and as illustrated in FIG. 11, includes two separate inclined surfaces 102a and 102b. A separation auxiliary member 103 which is fixed to be parallel with the inclined surfaces 102a and 102b is interposed between the inclined surfaces 102a and 102b. The separation auxiliary member 103 includes members with higher friction coefficients than the inclined surfaces 102a and 102b. Moreover, FIG. 11 is a plan view of the separation plate 102 and the separation auxiliary member 103 in a direction (refer to an arrow C) allowing viewing of the separation plate 102 illustrated in FIG. 10 from above.
In the feeding device 100, as the front end of the sheet S1 comes in contact with the inclined surfaces 102a and 102b and the separation auxiliary member 103, the sheet S1 receives a reaction force from the inclined surfaces 102a and 102b and the separation auxiliary member 103. Accordingly, the front end of the sheet S1 is able to be bent, and thereafter, the sheet S1 is conveyed upward along the inclined surfaces 102a and 102b due to the rotation of the feeding roller 105. Here, even through the sheet S is a sheet with a low rigidity, such as a thin paper, the sheet S1 is easily separated from other sheets by the separation auxiliary member 103.
A feeding device provided with, for example, the separation auxiliary member 103 in a part of an inclined surface on which sheets are conveyed is disclosed in Japanese Patent Application Laid-Open No. H11-011719 or 2003-054781. In the feeding device disclosed in Japanese Patent Application Laid-Open No. H11-011719, an insert is provided which projects from the inclined surface according to the rigidity of a sheet or recedes to a position flush with the inclined surface so as to be changed in shape. In the feeding device disclosed in Japanese Patent Application Laid-Open No. H11-011719, in a case where a sheet with high rigidity such as a thick paper is conveyed, the insert is pressed due to the rigidity of the sheet. Therefore, the reaction force (resistance) exerted on the sheet during conveyance is reduced as compared with a case where the insert projects from the inclined surface. Accordingly, a sheet feed failure of a sheet with high rigidity is prevented.
In a feeding device disclosed in Japanese Patent Application Laid-Open No. 2003-054781, a link mechanism for elevating a sheet feed tray is provided. In the feeding device disclosed in Japanese Patent Application Laid-Open No. 2003-054781, in a case where a sheet with low rigidity is conveyed, the link mechanism is lifted. Then, a separation pad with a higher friction coefficient than the inclined surface is disposed on a part of the inclined surface. On the other hand, in the case where a sheet with low rigidity is conveyed, the link mechanism is lowered. As described above, stable sheet feeding is implemented by selectively using the separation pad according to the rigidity of the sheet.
However, in the feeding device disclosed in Japanese Patent Application Laid-Open No. H11-101719, when a sheet with high rigidity is conveyed along the inclined surface, the insert and the sheet are not completely in non-contact with each other. This is because the insert recedes to be flush with the inclined surface and does not become hidden inside the inclined surface, although the front end of the sheet directly presses the insert. This always causes friction of the insert during conveyance of the sheet and thus is insufficient as a measure against sheet feed failure.
On the other hand, in the feeding device disclosed in Japanese Patent Application Laid-Open No. 2003-54781, when a sheet with high rigidity is conveyed along the inclined surface, the separation pad and the sheet are completely in non-contact with each other as a result of the link mechanism. However, the feeding device requires a large-scale mechanism for elevating the sheet feed tray, so that there is a problem in that costs are increased.